[aprssig] Lowercase callsigns in AX.25/APRS messages

[Andrew P.]

In debugging my APRS client, I have noticed a few (very few) stations using lower case in their callsigns. Is this legal? It's obviously possible, since they are out there. 

Since they exist, should my application:

1. Match on their callsign using case-insensitive matching or case-sensitive?

2. Force users of my application to enter their own callsigns in uppercase?

3. Forcibly upshift their callsigns in the headers of forwarded/digipeated messages and/or displayed status tables?

Example received from APRS-IS (I replaced my gateway's callsign with XXXXXX):

}kc2yu-sn>APKRAM,TCPIP,XXXXXX*:/171917z4041.78N/07359.46W$sn

Just curious how to handle these.

Andrew Pavlin, KA2DDO
Sent from my Verizon Wireless BlackBerry